1. Field of the Invention
The present invention relates to telecommunications and, in particular, to routing of calls in a number portability environment.
2. Background and Objects of the Present Invention
Ordinarily, subscriber directory numbers are geographic in that the subscriber directory number relates to a certain geographic area within the domain of the numbering plan. For example, in North America, the first six digits of the subscriber identify the particular switch that serves the directory number. The last four digits identify the actual subscriber within the switch.
The telecommunications network uses the information contained in the called directory number to route the call. This manner of routing calls requires the directory numbers to be tied to the serving switch as opposed to a subscriber. A subscriber who changes switches must change their directory number. If the directory number were not changed, a call to the subscriber would be routed to the wrong switch.
This is problematic for several reasons. Persons who have to change directory numbers because of relocation experience a certain degree of inconvenience brought on by having to notify others of their new directory number. This restriction also presents a major hurdle for mobile systems. Unlike a wire line, a mobile system subscriber does not belong to any one switch. Instead, the mobile subscriber is served by the switch in the area that the subscriber is currently roaming. A call terminating to a mobile subscriber cannot be terminated using the directory number.
To cope with this problem in the wireline telephone, an interface to telephone company databases (Service Control Points) has been developed which cross-references ported directory numbers with the proper routing information. When a call is placed to a portable directory number, the originating switch (the switch serving the calling party) sends a request to an intermediate switch (Signal Transfer Point) for a query to a respective Service Control Point to determine the proper routing information. Likewise, switches serving mobile phones, Mobile Switching Centers (MSC), in a wireless network maintain a similar system whereby calls terminated to mobile phone subscribers can be routed.
However, MSCs are not capable of accessing the Service Control Point (SCP) to determine the routing information of calls terminating to subscribers using the wireline network. One reason for this is that the communications protocol utilized by the SCP is based on an Advanced Intelligent Network (AIN) standard which cannot presently be used by MSCs. Consequently, the MSC routes the call to a portable directory number in the wireline network based on the information contained in the directory number. This, however, results in the call being routed improperly, inefficient use of network resources and longer connection times, because the switch serving the portable directory number cannot necessarily be deduced based on the information contained in the portable directory number.
What is desired, therefore, is a way to enable MSCs to determine the appropriate routing information for portable wireline directory numbers.
Accordingly, it is an object of the present invention to provide an improved system, method and apparatus for routing telephone calls.
It is also an object of the present invention to enable MSCs to determine the appropriate routing information for portable wireline directory numbers in an inexpensive manner.